Estradiol and progesterone alter the contractile response of the uterus to adrenergic nerve stimulation and catecholamaines. This study is designed to determine the mechanism by which these changes are effected. We have found that these hormones cause changes in the concentration of alpoha adrenergic receptors are present postsynaptically as two subtyupes alpha1 and alpha2 adrenergic receptors. We plan to characterize the physiological role of these receptor subtype and post-receptor response by sex steroids. In addition we will begin to study molecular mechanisms for the demonstrated change in alpha receptors caused by estrogen. These studies will provide information on the relationship of adrenergic receptors to smooth muscle contractility and how these are modulated by the hormonal environment and may suggest novel approaches to stimulation or inhibition of uterine contractility.